This protocol describes a multicenter expanded access open label safety study of recombinant humanized anti-p185 HER2 monoclonal antibody (rhuMAb HER2) in approximately 500 patients with HER2 overexpression who have relapsed following two or more cytotoxic chemotherapy regimens for metastatic breast cancer. Due to the very limited drug supply available, eligible patients will be randomly selected by lottery based on an enrollment assumption of 100 patients per quarter for five quarters. Geographically diversed centers will be involved in the study in order to allow widespread availability of this new agent. Following screening for eligibility, the National Center Institutes Treatment Referral Center will refer patietns to the closest participating center.